Over the last two decades, non-invasive, ultrasound-based techniques have been developed to extract tissue stiffness information. A main approach in ultrasound elasticity imaging is to estimate tissue strain caused by compression of bodily structures of interest. Stiff tissue has a high elasticity modulus and therefore shows less strain than soft tissue under applied compression force. By estimating tissue strain induced by applied compression, tissue stiffness information can be obtained.
The reason why researchers are interested in tissue stiffness is because they have found that abnormal cells, such as papillary adenocarcinoma, the most common thyroid cancer, is five times stiffer than normal thyroid tissue, and benign thyroid lesions are 1.7 times stiffer than normal fibroid tissue with a certain amount of compression force. Conventionally, finger palpation, which is used to search for abnormally stiff tissues, has been a primary tool for detecting thyroid nodules that may be abnormal.
To investigate ultrasound strain imaging of the thyroid, researchers applied external compression on the neck area and estimated the resulting strain from ultrasound signals. However, it has been reported that the quality of strain images and the resulting diagnostic performance are significantly affected by the pulsation of the carotid artery and out-of-plane motion during external free-hand compression. Without a solution to solve or reduce the problem, the strain images can be of poor quality, and it may not be possible to develop diagnostic machinery based on strain images.